01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - In a small saucepan over low heat, gently cook blueberries for 3 to 4 minutes, stirring until they burst and release juices. Lightly mash with a fork and let cool.
03 - In a large mixing bowl, beat softened butter and granulated sugar until light and fluffy, about 2 minutes.
04 - Add egg, vanilla extract, and lemon zest to the creamed mixture, beating until thoroughly combined.
05 - Mix in the cooled mashed blueberries until the batter is evenly tinted.
06 - In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
07 - Gradually add the dry mixture to the wet ingredients, mixing until just incorporated.
08 - If using, gently fold in white chocolate chips.
09 - Scoop tablespoon-sized portions of dough onto prepared baking sheets, leaving about 2 inches between each.
10 - Bake in preheated oven for 12 to 14 minutes, or until edges are set and centers are slightly soft.
11 - Allow cookies to cool on the sheets for 5 minutes, then transfer to a wire rack to cool completely.